1. Field of the Invention
The present invention relates to a forward direction power control method using a backward direction power control sub-channel for a mobile communication system, and in particular to a forward direction power control method using a backward direction power control sub-channel for a mobile communication system which is capable of rapidly and effectively controlling the power of a base station transmission signal using a backward direction power control sub-channel when performing an outer loop and inner loop in a mobile station of a mobile communication system using an IS-2000 CDMA(Code Division Multiple Access).
2. Description of the Background Art
Generally, as shown in FIG. 1, a mobile communication system using an IS-2000 CDMA includes a mobile station 1, a base station 2 for transmitting and receiving a data with the mobile station 1 and controlling a data wireless transmission and receiving operation with the mobile station 1, and a control station 3 for transmitting and receiving a data with the base station 2 and controlling a data transmission and receiving operation with the base station 2, and a switch station 4.
In the above-described mobile communication system, the forward direction power control operation is implemented by increasing the power of a base station transmission and receiving signal for transmitting to a mobile station which is located in an area in which it is difficult to transmit signals due to a bad signal transmission environment and decreasing the power of a base station transmission and receiving signal for transmitting to a mobile station which is located in an area in which a communication state is good.
The forward direction power control operation is one of the important CDMA techniques capable of transmitting a proper power level of a transmission and receiving signal at the base station, preventing a power consumption and maintaining a good communication quality.
The conventional forward direction power control is classified into two methods based on a band class. In the case that the band class is 0, a communication frame that a mobile station transmits to a base station is checked. As a result of the check, if an error frame exceeds a certain threshold value, a power measuring report message is transmitted to the base station, and the power control is performed based on a frame error ratio at a voice coder at a control station depending on the above-described message.
At this time, when the mobile station transmits a power measuring report message to the base station, the transmission state is in an error state. Therefore, it means that the error frame corresponds to an error threshold value (a corresponding parameter: pwr_rept_thesh) among the received frames and to a normal state. Therefore, it means that the normal frame which does not have an error frame is transmitted to the mobile station by the number of 2(the number of the power control report frames/2)xc3x975.
Namely, in the case that the frame is in the normal state, when the power measuring report message is not received or the frame of the normal state is continuously maintained after the base station transmits an initial communication frame, in the voice coder block, the down degree (a corresponding parameter: fast_down_delta) of the digital gain is obtained at a period of the timer expiration time (a corresponding parameter: fast_down_time) of the fast down mode for thereby decreasing the power of the transmission and receiving signal of the base station.
In addition, in the case that the frame is in an error state, when the number of the errors is below the error threshold value ( a corresponding parameter: pwr_rept_thresh), the digital gain(a corresponding parameter: small_up_delta) is increased based on a small degree. In the case of the error threshold value, the digital gain (a corresponding parameter: small_up_delta) is increased based on a large degree.
Since the power up and down degrees is different depending on the frame state, the above-described parameter is an important factor for determining the performance of the system for the power control.
In the conventional art, since the number of the power control report frames is 7 (threshold value), about 57 frames are used. Therefore, the power control is performed at a period of about 1.14 seconds for thereby implementing a slow control.
In the case that the band class is 1, the power control is performed using a frame error indication bit. At this time, the error report is performed based on the frame unit of 20 m seconds. Therefore, it is possible to implement a rapid power control compared to the case that the class is 0.
Namely, the frame state is checked whenever the mobile station receives a communication frame, and the frame state information(a icon normal state: 0, and an error state: 1) is allocated to the backward direction communication frame and is transmitted to the control station through the base station. In the control station, the receiving frame is checked. In the case that the frame error indication but is 0, the digital gain of the channel is decreased, and in the case that the frame error indication bit is 1, the digital gain is increased, and a constant frame error ratio is maintained for thereby controlling the power of the base station transmission signal.
In the forward direction power control in which the band class is 1, a value smaller than the up and down value of the forward direction power control in which the band class is 0 is set for thereby implementing an effective power control.
However, In the conventional forward direction power control method based on the band class, the power of the base station transmission signal is adjusted after the control station receives a frame error ratio of the forward direction channel for thereby causing a power control delay. In addition, the slow power control is performed at a period of 20 mxcx9c1.14 sec. this case, it is difficult to rapidly cope with a channel environment and forward direction wireless environment, and it is impossible to effectively control the power of the base station transmission signal. Furthermore, an over power consumption of the transmission signal of the base station occurs, and the capacity of the power is decreased.
Accordingly, it is an object of the present invention to provide a forward direction power control method using a backward direction power control sub-channel for a mobile communication system which is capable of rapidly and effectively controlling the power of a base station transmission signal using a power control, sub-channel in a backward direction pilot channel when performing an outer loop and inner loop in a mobile station of a mobile communication system which adapts an IS-2000 CDMA method and rapidly coping with a channel environment and forward direction wireless environment for thereby decreasing the power of a transmission signal of the base station and increasing the capacity of the system.
In order to achieve the above objects, there is provided a forward direction power control method using a backward direction power control sub-channel for a mobile communication system which includes a channel information and channel transmission and receiving step for transmitting and receiving a channel information for performing an inner loop and a channel corresponding to the channel information for a forward direction power control between a mobile station and a base station, a channel-based receiving power measuring step for measuring a channel-based current receiving power when a mobile station receives a channel in the channel information and channel transmission and receiving step, an outer Loop operation step for determining a channel-based reference receiving power that the mobile station receives as the mobile station performs an outer loop at a period of 20 ms after the channel-based receiving power measuring step, an inner loop operation step for performing an inner loop at a period of 1.25 ms by the mobile station after the outer loop operation step and comparing the current channel-based receiving power measured in the channel-based receiving power measuring step and the channel-based reference receiving power determined in the outer loop operation and determining an information for requesting a power up or down of the base station transmission signal and allocating the determined information to a PCB of the backward direction power control sub-channel, a backward direction power control sub-channel transmission and receiving and power control step for transmitting and receiving a backward direction power control sub-channel including the PCB having an information allocated in the inner loop operation between the mobile station and the base station and controlling the power of the base station transmission signal in accordance with the information allocated to the PCB of the backward direction power control sub-channel, an outer loop report message transmission state determination step in which the mobile station is determined to transmit the outer loop report message to the base station after the backward direction power control sub-channel transmission and receiving and power control step, an outer loop report message transmission and power control step for transmitting and receiving an outer loop report message between the mobile station and the base station in the case that the result determined in the outer loop report message transmission state determination step corresponds to the outer loop report message transmission permission and performing the power control of the base station transmission signal with respect to the base station transmission signal, and an outer loop report message non-transmission step for performing the channel information and channel transmission and receiving step in a state that the mobile station does not transmit the outer loop report message to the base station in the case that the result determined in the outer loop report message transmission state determination step does not correspond to the outer loop report message transmission permission and performing the next steps.
Additional advantages, objects and features of the invention will become more apparent from the description which follows.